The present invention relates to improvements in multi-layer gaskets.
Gaskets are often used as a seal between mating mechanical components. One common application involves gasket placement between the engine block and cylinder head of an internal combustion engine. Cylinder head gaskets typically extend around the cylinder bores to provide a combustion seal, maintaining the high temperature gases of combustion within the cylinder bores. At the same time, the gaskets also seal fluid flow openings such as coolant and oil openings to prevent undesirable mixing. In addition, such gaskets prevent leakage by sealing the areas around the bolts which connect the cylinder head and engine block. The gasket bears the load from a bolted connection of the mechanical components and relies upon that load to provide a seal.
To function reliably in the environment of an internal combustion engine, the gaskets must be resistant to wear resulting from fretting corrosion, heat, and mechanical stress, particularly around cylinder bores. Thus, it is desirable to have a lubricous high temperature coating, which is "slippery" with a low coefficient of friction, protecting those portions of a gasket surrounding each cylinder bore. Simultaneously, however, a gasket must ensure an effective fluid seal around fluid flow openings. Thus, it is also desirable to have an elastomeric coating applied to those portions of the gasket surrounding fluid flow openings. It has been difficult to achieve these goals in a single gasket, particularly since it is preferable that the elastomeric coating be spaced away from those portions of the gasket surrounding cylinder bores.
Multi-layer metal gaskets have been developed which have the above-described coatings applied as indicated. Such gaskets have been difficult and expensive to produce. Typically, the layers of such gaskets have been blanked and configured with coatings selectively applied to or masked off from the rest of a side of a particular layer. Difficulties in masking and selectively applying protective coatings to layers have limited the effectiveness of such gaskets.
It is also known to utilize separate plates carrying the high temperature and elastomeric coatings, with the elastomeric coated plates being spaced away from the cylinder bores. The varying thickness of various portions of such a gasket has created undesirable load balances between the various seals, causing problems such as insufficient sealing stress which may result in gasket failure.
In short, mechanical limitations and cost has restricted the ability to provide multi-layer gaskets with varying characteristics depending upon the nature of the seal required to be effected at a particular location.